Quick/useful post (hopefully).
I have a friend - let's call him David because that is in fact his name - who dabbles in iOS app development. As we're been friends for about thirty years or so I often gamely volunteer to test out whatever he's working on. Not every app actually makes it all the way to completion (and even then only a couple have made their way to the App Store), largely because he has another actual job and has the kind of work ethic that would make Thomas Edison look like he was just phoning it in every day.
iOS is great about memory management and graceful resource use on well-written apps. It's not so great when you're running a very rough approximation of an app, and your battery life and cellular data bill can reflect that accordingly. Quitting an app in iOS isn't a big deal, but it can be advantageous to prevent an app from using Cellular data. It takes a little digging around, but can be done thus:
First fire up the Settings app:
...then scroll down and selectively turn on/off cellular data for each app:
Et Voila! My friends Apps are way down the list and not revealed (to protect the innocent and also myself from the endless barrage of abuse that he'd doubtless hurl at me), but since tweaking those settings I've noticed some appreciable bumps in battery life that have made my role as a test subject a little easier...